AT&T supplies information on international calls that travel over its network, including ones that start or end in the U.S., under a voluntary contract with the U.S. Central Intelligence Agency, The New York Times reported Thursday.

The CIA pays the carrier more than US$10 million annually for the data, including the date, duration and numbers involved in a call, the Times said, citing unnamed government officials. The calls include ones that are made by customers of other carriers but travel partly on AT&T's network. For calls with a U.S. participant, AT&T doesn't tell the CIA the identity of the U.S. caller and masks several digits of the domestic number, the report said.

The CIA isn't allowed to conduct domestic spying. However, the agency can hand over the masked numbers to the Federal Bureau of Investigation, which can subpoena AT&T for the uncensored data, the Times said. The FBI, in turn, sometimes shares information with the CIA about the U.S. participant in a call.

The latest report is likely to heighten concerns about the U.S. government's surveillance of voice and data communications around the world. Disclosures made by former National Security Agency contractor Edward Snowden starting earlier this year have helped to spark calls for reform of surveillance practices and rankled several U.S. allies.

In an emailed statement, the CIA said it doesn't comment on alleged intelligence sources or methods.

"The CIA protects the nation and upholds the privacy rights of Americans by ensuring that its intelligence collection activities are focused on acquiring foreign intelligence and counterintelligence in accordance with U.S. laws," said Dean Boyd, director of the CIA Office of Public Affairs. The agency is subject to oversight from multiple entities, he said.

AT&T does not comment on questions concerning national security, spokesman Mark Siegel said in a statement emailed to IDG News Service.

"In all cases, whenever any governmental entity anywhere seeks information from us, we ensure that the request and our response are completely lawful and proper," Siegel wrote. "We ensure that we maintain customer information in compliance with the laws of the United States and other countries where information may be maintained. Like all telecom providers, we routinely charge governments for producing the information provided."